This invention relates to a print head for use in printers having cleaning features.
Ink jet printers produce images on a receiver by ejecting ink droplets onto the receiver in an image wise fashion. The advantages of non-impact, low-noise, low energy use, and low cost operation in addition to the capability of the printer to print on a receiver medium such as a plain paper are largely responsible for the wide acceptance of ink jet printers in the marketplace.
Many types of ink jet printers have been developed. One form of ink jet printers the xe2x80x9ccontinuousxe2x80x9d ink jet printer. Continuous ink jet printers generate stream of ink droplets during printing. Certain droplets are permitted to strike a receiver medium while other droplets are diverted. In this way, the continuous ink jet printer can controllably define a flow of ink droplets onto the receiver medium to form an image. One type of continuous ink jet printer uses electrostatic charging tunnels that are placed close to the stream of ink droplets. Selected ones of the droplets are electrically charged by the charging tunnels. The charged droplets are deflected downstream by the presence of deflector plates that have a predetermined electric potential difference between them. A gutter may be used to intercept the charged droplets, while the uncharged droplets are free to strike the receiver.
Another type of ink jet printer is the xe2x80x9con demandxe2x80x9d ink jet printer. xe2x80x9cOn demandxe2x80x9d ink jet printers eject ink droplets only when needed to form the image. In one form of xe2x80x9con demandxe2x80x9d ink jet printer, a plurality of ink jet orifices is provided and a pressurization actuator is provided for every nozzle. The pressurization actuators are used to produce the ink jet droplets. In this regard, either one of two types of actuators are commonly used: heat actuators and piezoelectric actuators. With respect to heat actuators, a heater is disposed in the ink jet orifice and heats the ink. This causes a quantity of the ink to phase change into a gaseous bubble and raise the internal ink pressure sufficiently for an ink droplet to be expelled onto the recording medium.
With respect to piezoelectric actuators, a piezoelectric material is provided for every nozzle. The piezoelectric material possesses piezoelectric properties such that an applied electric field will produce a mechanical stress in the material. Some naturally occurring materials possessing these characteristics are quartz and tourmaline. The most commonly produced piezoelectric ceramics are lead zirconate titanate, barium titanate, lead titanate, and lead metaniobate. When these materials are used in an ink jet print head, they apply mechanical stress upon the ink in the print head to cause an ink droplet to be ejected from the print head.
Inks for high speed ink jet printers, whether of the xe2x80x9ccontinuousxe2x80x9d or xe2x80x9con demandxe2x80x9d type, must have a number of special characteristics. For example, the inks should incorporate a nondrying characteristic, so that drying of ink in the ink ejection chamber is hindered or slowed to such a state that by occasional xe2x80x9cspittingxe2x80x9d of ink droplets, the cavities and corresponding orifices are kept open.
Moreover, the ink jet print head is exposed to the environment where the ink jet printing occurs. Thus, the previously mentioned orifices and print head surface are exposed to many kinds of airborne particulates. Particulate debris may accumulate on the print head surface surrounding the orifices and may accumulate in the orifices and chambers themselves. Also, ink may combine with such particulate debris to form an interference burr that blocks the orifice or that alters surface wetting to inhibit proper formation of the ink droplet. Of course, the particulate debris should be cleaned from the surface and orifice to restore proper droplet formation.
Ink jet print head cleaners are known. An ink jet print head cleaner is disclosed in U.S. Pat. No. 4,970,535 titled xe2x80x9cInk Jet Print Head Face Cleanerxe2x80x9d issued Nov. 13, 1990 in the name of James C. Oswald. This patent discloses an ink jet print head face cleaner that provides a controlled air passageway through an enclosure formed against the print head face. Air is directed through an inlet into a cavity in the enclosure. The air that enters the cavity is directed past ink jet apertures on the head face and out an outlet. A vacuum source is attached to the outlet to create a sub-atmospheric pressure in the cavity. A collection chamber and removable drawer are positioned below the outlet to facilitate disposal of removed ink. However, the use of heated air is not a particularly effective medium for removing dried particles from the print head surface. Also, the use of heated air may damage fragile electronic circuitry that may be present on the print head surface.
Cleaning systems that use a cleaning fluid such as an alcohol or other solvent have been found to be particularly effective when used to clean print heads. This is because the solvent helps to dissolve the ink and other contaminants that have dried to the surface of the print head. However, it is not a simple matter to apply a cleaning fluid to a print head to clean the print head or to remove the cleaning fluid once it has been used.
One way to use a solvent to clean a print head is known as wet wiping. In wet wiping, a cleaning fluid is applied to the print head and a wiper is used to clean the cleaning fluid and contaminants from the print head. Examples of various wet wiping embodiments are found in U.S. Pat. No. 5,914,734 by Rotering et al. Each of these embodiments uses a cleaning station to apply a metered amount of cleaning fluid to the print head and to wipe cleaning fluid and contaminants from the print head. However, wipers can damage the fragile electronic circuitry and Micro Electro-Mechanical Systems (MEMS) that may be present on the print head surface.
Another ink jet print head cleaner is disclosed in commonly assigned U.S. Pat. No. 4,600,928 by Braun et al. Braun et al. shows a continuous ink jet printing apparatus having an ultrasonic print head cleaning system. During cleaning, the print head is moved to a cleaning area and a cleaning station is fixed to the print head. Once that the print head is so positioned, a meniscus of ink is supported proximate to the ink droplet orifices, a charge plate and/or an ink catcher surface. Cleaning is then accomplished by ultrasonically vibrating the meniscus. This cleaning can be enhanced by providing a fluid pressure differential in the meniscus to cause the meniscus to enter into orifices to be cleaned and to be released from the orifices. Once that the cleaning operation is completed, ink from the print head is ejected into a sump in the cleaning station.
U.S. Pat. No. 5,574,485 to Anderson et al. describes a cleaning station having a jet to define a flow of a cleaning fluid at a print head forming a meniscus bridge of cleaning fluid between the print head and the jet. Anderson et al. teaches that the print head can be cleaned the agitating the fluid by use of an ultrasonic vibrator and removing the fluid by way of a pair of vacuum sources disposed on the cleaning station and flanking the jet.
It will be noted that in the prior art, the supply of the cleaning fluid that is used to clean the print head does not come from a cleaning fluid source that is contained within the print head. In Braun, et al., ink is used as a cleaning fluid and a fluidic connection is defined between the print head and the supply of ink. In Rotering, et al., and Anderson et al. the cleaning station supplies the cleaning fluid used for cleaning the print head.
It will also be noted that in the prior art, a cleaning station is required to receive cleaning fluid and any entrained contaminants that are removed from the print head.
Thus, it is an object of this invention to provide a self-cleaning printer and self-cleaning print head with a supply of cleaning fluid contained within the print head.
It is a further object of this invention to provide a self-cleaning printer and self-cleaning print head that do not require a cleaning station to receive cleaning fluid and contaminants from the surface of a print head after cleaning operations.
According to one embodiment of the present invention, a print head comprises a print head body defining an interior chamber and an orifice plate. The orifice plate defines a cleaning fluid orifice, an ink jet orifice and a drain orifice and further defines an outer surface between the orifices. A supply of pressurized cleaning fluid is disposed in said interior chamber and is connected to the cleaning fluid orifice. A fluid return is disposed in said interior chamber and is connected to the drain orifice. During cleaning operations, the supply of pressurized cleaning fluid defines a flow of a cleaning fluid from the cleaning fluid orifice and onto said outer surface and the drain orifice receives cleaning fluid from the outer surface and channels the cleaning fluid into the fluid return.
According to another embodiment, a printer is provided having a print head with a print head body defining an interior chamber and further defining an orifice plate having an outer surface with the outer surface having a cleaning orifice and a drain orifice defined therethrough. A supply of a pressurized cleaning fluid is disposed in said interior chamber and connected to said cleaning orifice. A cleaning member is provided to clean the outer surface. During cleaning, the supply of cleaning fluid causes a flow of cleaning fluid onto the outer surface and said cleaning member uses the cleaning fluid to clean the outer surface. A fluid return is disposed within said interior chamber, and connected to said drain orifice. The drain orifice receives cleaning fluid from the outer surface and channels the cleaning fluid into the fluid return. According to one embodiment, the cleaning member moves the used cleaning fluid into the drain orifice.